Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$124.27	10.274%	$137.0375	$137.04	$137.05	$137.00
Purchase #2	$71.75	8.190%	$77.6263	$77.63	$77.65	$77.60
Purchase #3	$46.88	13.368%	$53.1469	$53.15	$53.15	$53.10
Purchase #4	$53.37	9.539%	$58.461	$58.46	$58.45	$58.50
Purchase #5	$108.32	9.786%	$118.9202	$118.92	$118.90	$118.90
Purchase #6	$50.86	10.712%	$56.3081	$56.31	$56.30	$56.30
Purchase #7	$108.88	13.343%	$123.4079	$123.41	$123.40	$123.40
7 purchase totals =	$564.33		$624.9079	$624.92	$624.90	$624.80